Low hazard corrosion inhibitors and cleaning solutions using quaternary ammonium salts

ABSTRACT

The present invention is directed to methods for preparing quaternary ammonium salts, particularly pyridinium and quinolinium salts. By preparing these salts in a solvent selected from the group consisting of propylene glycols, propylene glycol ethers and mixtures thereof, the production of undesirable by-products and contamination of the product with undesirable solvents are minimized, if not eliminated. Using the preparation methods of the present invention low hazard corrosion inhibitors and aqueous cleaning solutions using these inhibitors may be prepared. In fact, by preparing dodecyl pyridinium bromide in dipropylene glycol methyl ether as the solvent, a particularly desirable corrosion inhibitor characterized by a low toxicity and a high flash point has been prepared. The present invention thus provides the safer corrosion inhibitors and cleaning solutions long sought by industrial cleaning services.

This application is a divisional of U.S. patent application Ser. No.09/250,854, filed Feb. 17, 1999, and now U.S. Pat. No. 6,118,000, whichis a division of U.S. patent application Ser. No. 08/742,290, filed Nov.4, 1996; and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to methods for preparingquaternary ammonium salts and low hazard corrosion inhibitors usingthose salts. More specifically, the present invention is directed tomethods particularly useful for producing pyridinium and quinoliniumsalts, to low hazard corrosion inhibitors using those salts and toaqueous cleaning solutions using those inhibitors.

2. Description of the Background

Scale comprised of insoluble salts is typically found on the surface ofall types of metal equipment in which water is evaporated or heattransfer occurs. These salt deposits are particularly undesirablebecause of their negative impact on the heat transfer efficiency of theequipment. Because the equipment loses heat transfer efficiency as thesedeposits build up, it is necessary to periodically clean the equipmentto remove the deposits. Industrial cleaning service companies oftenprovide the required cleaning services for this equipment, e.g., theboilers and heat transfer equipment of utilities and industrial plants.

The undesirable scales which must be removed generally comprise calciumand magnesium salts deposited during the evaporation of hard water.Exemplary of these scales are deposits including calcium carbonate,calcium sulfate, calcium phosphate and calcium oxylate. While calciumand magnesium salts comprise the majority of these deposits, salts ofother materials may be encountered. Scales high in iron content, e.g.,scales including magnetite or hematite, often must be cleaned.

The conventional cleaning operations rely upon the circulation ofaqueous cleaning solutions through the equipment, e.g., boilers, heatexchangers and associated piping in an effort to dissolve the saltdeposits comprising the scale. Often, these cleaning solutions areheated to temperatures above the boiling point of water. In many earlycleaning efforts highly acidic solutions were circulated through theequipment to dissolve the calcium and magnesium salts found in the hardwater scale and the magnetite and hematite deposits encountered in highiron scales. As cleaning operations became more sophisticated, solutionscontaining agents capable of complexing the metals associated with thedeposited salts were circulated in order to loosen and dissolve thescale. Ammonia has been used as an alkaline complexing agent for thispurpose. See, e.g., the disclosure in U.S. Pat. No. 3,413,160. Morerecent developments have included complexing agents based uponethylenediaminetetraacetic acid and related compounds.

Because many of these cleaning solutions are, themselves, corrosive tothe metal components of the equipment being cleaned, the solutions mustinclude appropriate corrosion inhibitors. For example, aliphaticpyridinium and quinolinium salts, together with sulphur-containingcompounds, have been employed successfully as corrosion inhibitors inthese solutions. See, e.g., the disclosure in U.S. Pat. No. 4,637,899which is incorporated herein by reference. While these corrosioninhibitors provide the desired protection of the metal surfaces, theyare often contaminated with unsafe and/or toxic byproducts, e.g.,solvents and unreacted. reactants, resulting from the methods by whichthey were prepared. Accordingly, these corrosion inhibitors and cleaningsolutions produced therefrom can present dangers to the employeesworking with them. Another danger associated with the use of thesecorrosion inhibitors is the low flash point, often less than 100° F.,resulting from the solvents and resistants which were used in theirmanufacture. Still another danger may result from the toxicity of itssulfur-containing compounds employed in these corrosion inhibitors. Forexample, ethylene glycol monobutyl ether is a toxic chemical used as asolvent and carried along with the aliphatic pyridinium salts used inthe methods and corrosion inhibitors disclosed in the '899 patent.Thiourea is an undesirable sulfur-containing compound typically used inthese inhibitors and methods.

As environmental and worker safety concerns have increased, the need toemploy less toxic corrosion inhibitors and cleaning solutions hasincreased. Further, as OSHA requirements and worker safety issues haveevolved, the benefits of employing corrosion inhibitors and cleaningsolutions with higher flash points has become clear. The industrialcleaning service industry has continued to seek improved corrosioninhibitors and cleaning solutions for use in commercial, scale cleaningoperations. The known methods and solutions have not solved theseproblems. Thus, there has been a long felt but unfulfilled need in theindustrial cleaning service industry for less toxic and safer corrosioninhibitors and cleaning solutions. The present invention solves thoseneeds.

SUMMARY OF THE INVENTION

The present invention is directed to methods for preparing quaternaryammonium salts and particularly pyridinium and quinolinium salts. Thesemethods are particularly useful in preparing low hazard corrosioninhibitors characterized by low toxicity and high flash points. Theselow hazard corrosion inhibitors are particularly useful in aqueouscleaning solutions for safely and effectively removing scale depositsfrom the interior of boilers and heat exchangers.

In the methods of the present invention a quaternary ammonium salt isprepared by contacting a tertiary ammonium compound with a secondcompound having the formula RX where R is aliphatic, substitutedaliphatic or alkyl aryl and X is an anion. Preferably R is selected fromthe group consisting of alkyl and alkyl aryl moieties having from about6 to about 18 carbon atoms and X is a halide, most preferably chlorideor bromide. The foregoing compounds are reacted in a solvent selectedfrom the group consisting of propylene glycols, propylene glycol ethersand mixtures thereof, most preferably dipropylene glycol methyl ether.The reaction is conducted at a temperature greater than about 65° C.,preferably in the range of about 75° C. to about 125° C. Optionally, thereaction may proceed in the presence of water. In its most preferredembodiment, the present invention comprises a method for preparingdodecyl pyridinium bromide by contacting pyridine with dodecyl bromidein dipropylene glycol methyl ether at a temperature above about 65° C.

The foregoing methods of the present invention produce mixtures ofreaction product and solvent characterized by lower toxicity thanmixtures prepared by conventional methods for preparing similarquaternary ammonium salts. Accordingly, salts prepared in accord withthe present invention may be used to prepare improved, low hazardcorrosion inhibitors. Not only do such corrosion inhibitors exhibitlower toxicity, but they also are characterized by higher flash pointsthan for similar inhibitor compositions prepared by prior methods. Theseimproved corrosion inhibitors may be used to prepare safer aqueouscleaning solutions.

A low hazard composition useful for inhibiting corrosion of steelcontacted by organic acids, chelating agents or sulfuric acid maycomprise the reaction product of the foregoing methods, asulfur-containing compound and a nonionic surfactant. Thesecorrosion-inhibiting compositions may be prepared in the solvent inwhich the reaction product was prepared, in water or in a mixture ofboth. Particularly useful corrosion inhibitors may comprise 20-50percent-by-weight of a mixture of the quaternary ammonium compoundprepared by the foregoing methods of the present invention and thesolvent used in preparing that compound, about 1-10 percent-by-weight ofa sulfur-containing compound and about 0-10 percent-by-weight of anonionic surfactant. The balance of the corrosion inhibitor compositionmay comprise water, the solvent or mixtures thereof. Not only are thesecorrosion inhibitors less toxic, but they are safer to handle, typicallyhaving flash points at least about 140° F. Such corrosion inhibitors arecharacterized by both lower toxicity and higher flash point than similarcompositions prepared by prior methods. These improved qualities may beattributed to the use of propylene glycol and propylene glycol ether asreaction solvents.

In a final aspect of the present invention, improved aqueous cleaningsolutions employing the quaternary ammonium salts produced by theforegoing methods are disclosed. Typical of these solutions are aqueouscleaning solutions having a pH from about 1-10 and comprising at leastone organic, acid selected from the group consisting of alkylenepolyamine polyacetic acids, hydroxyacetic acids, citric acid andmixtures or salts thereof, together with an effective amount of acorrosion inhibitor including quaternary ammonium salt prepared inaccord with the methods of the present invention. In another aspect ofthe present invention, aqueous cleaning solutions comprising at leastone acid selected from the group consisting of sulfuric acid,hydrochloric acid and phosphoric acid, together with an effective amountof a corrosion inhibitor including a quaternary ammonium salt producedby the methods of the present invention, are disclosed. The cleaningsolutions of the present invention are safer than those produced usingprior methods.

The present invention provides methods for producing quaternary ammoniumsalts useful in applications where reduced hazard levels, e.g., lowtoxicity, are required. The present invention provides methods forproducing improved corrosion inhibitors characterized by lower toxicityand higher flash points. Accordingly, these corrosion inhibitors providehealth and safety benefits to the industrial cleaning industry wherethey may be used to formulate industrial cleaning solutions.

Thus, the long felt but unfulfilled need in the industrial cleaningindustry for safer corrosion inhibitors and aqueous cleaning solutionshas been met. These and other meritorious features and advantages of thepresent invention will be more fully appreciated from the followingdetailed description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and intended advantages of the present invention will bemore readily apparent by the references to the following detaileddescription in connection with the accompanying drawings, wherein:

FIGS. 1 to 28 are graphical representations of test data, e.g., reactioncoordinates and corrosion tests, for the claimed methods for preparingquaternary ammonium salts and for corrosion inhibitors using thesesalts.

While the invention will be described with reference to the presentlypreferred embodiments, it will be understood that it is not intended tolimit the invention to those embodiments. On the contrary, it isintended to cover all alternatives, modifications and equivalents as maybe included in the spirit of the invention as defined in the appendedclaims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed in its broadest sense to methods forpreparing quaternary ammonium salts by contacting a tertiary ammoniumcompound with a second compound having the formula RX where R isaliphatic, substituted aliphatic or alkyl aryl and X is an anion. In thepresent invention the contacting proceeds in a solvent selected from thegroup consisting of the propylene glycols, propylene glycol ethers andmixtures thereof. In the most preferred method, pyridine is contactedwith dodecyl bromide in dipropylene glycol methyl ether (DPM) to producedodecyl pyridinium bromide (DDPB) and mixtures thereof in DPM.

Quaternary ammonium salts prepared in accord with the present inventionand mixtures of those salts in the solvent of preparation arecharacterized by a lower toxicity and higher flash point than similarsalts and mixtures prepared by methods using conventional solvents,e.g., isopropanol (IPA), ethylene glycol and ethylene glycol monobutylether (EB). The methods of the present invention are particularly usefulfor producing quaternary ammonium salts, most particularly DDPB, for usein applications requiring lower toxicity and higher flash points. Whilethere are applications for those products in cosmetics, toiletries andother personal hygiene products, DDPB and mixtures thereof with DPM havebeen found particularly useful in the preparation of improved corrosioninhibitors and aqueous cleaning solutions including those inhibitors.

A conventional corrosion inhibitor and aqueous cleaning solutions usingthat inhibitor were disclosed in U.S. Pat. No. 4,637,899. While thecleaning solutions described therein have been quite successful, thosein the industrial cleaning service would welcome cleaning solutionshaving lower toxicity and higher flash points. A preferred cleaningsolution prepared in accord with the disclosure of the '899 patent andusing conventionally prepared DDPB is characterized by a low flash point(88° F.) and includes isopropanol and two components, thiourea and EB,both considered toxic. Lethal dose toxicity values for thiourea and EB,respectively, are only 125 mg/kg and 1500 mg/kg for LD₅₀. (oral rats).Thiourea also has been listed on the registers of the National ToxicityProgram and the International Agency for Research on Cancer was apossible cancer causing agent in animals. Isopropanol used both in thepreparation of DDPB and as a solubilizing alcohol is relatively toxic,with as little as 100 ml being fatal to humans. Accordingly, it would bedesirable to replace these components with less toxic components withoutadversely affecting the corrosion-inhibiting characteristics of thecomposition.

It was well known that propylene glycol and propylene glycol ethers havemuch lower toxicities than ethylene glycol and corresponding ethyleneglycol ethers. The propylene glycols and propylene glycol ethers alsohave relatively high flash points, e.g., greater than 150° F. However,it was not clear that quaternary ammonium salts, and in particular DDPB,could be synthesized in propylene glycol or propylene glycol ethers, anecessary step in eliminating isopropanol as a reaction solvent andcomponent of the finished corrosion inhibitors.

Propylene glycol and its ethers are generally characterized by higherflash points than the solvents used in the prior methods. For example,the flash points of propylene glycol (PG) and dipropylene glycol methylether (DPM), respectively, are 210° F. and 175° F. More importantly,propylene glycol and its ethers are significantly less toxic thanisopropanol or ethylene glycol monobutyl ether. For example, the lethaldose toxicity values, LD₅₀ (oral rats), for PG and DPM are very high at20,000 mg/kg and 5130 mg/kg, respectively. Thus, propylene glycol andits ethers would not only produce compositions with higher flash pointsbut, more significantly, compositions with markedly lower toxicity.

In the methods of the present invention, a quaternary ammonium salt isprepared by contacting a tertiary ammonium compound with a secondcompound having the formula RX where R is aliphatic, substitutedaliphatic or alkyl aryl and X is an anion. The choice of anion is notcritical and may be varied for convenience. Examples of suitable anionsinclude chloride, bromide, iodide, nitrate, methyl sulfate, bisulfate,tosylate, acetate, benzoate, dihydrogen phosphate and the like. Bromideand chloride are the preferred anions.

In a more preferred embodiment, the tertiary ammonium compound isselected from the group consisting of aromatic ammonium compounds, morepreferably, pyridine, alkyl pyridine, quinoline, alkyl quinoline andmixtures thereof. Even more preferably, the tertiary ammonium compoundmay be represented by the formula

wherein each R′₅ independently is —H, —OH, —OR, —OROH, alkyl, alkenyl,alkynyl or halo. In the more preferred embodiment, the second compoundhaving the formula RX is selected from the alkyl halides and the alkylaryl halides having from about 6 to about 18 carbon atoms. Morepreferably, this second compound is selected from the benzyl halides,naphthyl halides and alkyl halides having from about 7 to about 16carbon atoms.

In the most preferred embodiments, the tertiary ammonium compound ispyridine, quinoline or a mixture thereof while the second compound is analkyl bromide, an alkyl aryl chloride or a mixture thereof. Mostpreferably, the tertiary ammonium compound is pyridine while the secondcompound is dodecyl bromide.

In the present invention, the contacting proceeds in a solvent selectedfrom the group consisting of propylene glycol, propylene glycol ethersand mixtures thereof. While propylene glycol may be used, the propyleneglycol ethers are preferred. More preferred are the propylene glycolaliphatic and aromatic ethers, particularly those wherein the aliphaticsubstituent has from 1 to 4 carbon atoms or the aromatic substituent isphenyl. Exemplary propylene glycol ethers include propylene glycolmethyl ether, dipropylene glycol methyl ether, tripropylene glycolmethyl ether, propylene glycol phenyl ether, propylene glycol methylether acetate and dipropylene glycol monomethyl ether acetate.

Water may optionally be added as an additional solvent during thecontacting step. The importance of the solvent in quaternizationreactions is well known. These reactions usually proceed more quickly inpolar solvents than in nonpolar solvents due to the formation of ions asthe reactions proceed. While polar molecules, e.g., the glycol ethersand water, are excellent solvents, there are several problems with thesechemicals. If separation of the quaternary salt is desired, the polarsolvents can be difficult to remove from the products. While thepresence of water accelerates the reaction, water may also react withthe alkyl bromide to form an alcohol and hydrogen bromide, thus reducingthe yield of the reaction. Thus, caution must be taken with respect tothe addition of water.

The preparation of the quaternary ammonium salts is conducted at atemperature greater than about 65° C., preferably from about 75° C. toabout 125° C. In the presently most preferred embodiment, pyridine anddodecyl bromide are contacted in dipropylene glycol methyl ether atabout 110° C. to about 115° C.

Quaternary ammonium salts prepared by the foregoing methods may be usedas components of low hazard corrosion inhibitor compositions useful forinhibiting the corrosion of steel contacted by organic acids, inorganicacids and chelating agents. Generally, these corrosion-inhibitingcompositions will include about 20-50 percent-by-weight of a mixture ofthe quaternary ammonium salt and solvent prepared in accord with theforegoing procedures by reacting a tertiary ammonium compound with asecond compound having the formula RX where R is aliphatic, substitutedaliphatic or alkyl aryl and X is an anion and the solvent is selectedfrom the group consisting of the propylene glycols, propylene glycolethers and mixtures thereof. The tertiary ammonium compound and secondcompound RX are preferably added in about equal molar ratios. The weightratio of quaternary ammonium salt to solvent in the final reactionmixture, while preferably about 1.5 to 1, may be in the range of about0.5 to 1 to about 2.0 to 1.

These corrosion inhibitor compositions include about 1-10percent-by-weight of a sulphur-containing compound, preferably acompound where sulfur is in the −2 oxidation state. Thesulfur-containing compound is also selected for its low toxicity. Thesulfur-containing compound enhances the corrosion-inhibiting protectionafforded by the quaternary ammonium salt component of the corrosioninhibitor. The sulfur-containing compound is employed in an amount thatis sufficient to improve the protection afforded by the quaternaryammonium salt. Typically, improved protection is achieved by includingat least about 0.2 moles of the sulfur-containing compound per mole ofthe quaternary ammonium salt. The corrosion inhibitor composition of thepresent invention preferably includes from about 0.2 to about 2 moles ofsulfur-containing compound per mole of quaternary ammonium salt.Exemplary sulphur compounds include the thiocyanate salts,mercaptoacetic acid and its salts, diethyl thiourea, dibutyl thiourea,diethyl dithio carbamic acid, its salts and methyl derivatives, trithiocarbamic salts and mixtures thereof. Most preferably, thesulphur-containing compound is mercaptoacetic acid, diethyl thiourea orammonium thiocyanate and mixtures thereof.

It is desirable, but not necessary, to employ a surfactant in thecorrosion inhibitor compositions of the present invention. An individualsurfactant or a mixture of several surfactants may be used. Exemplarynonionic surfactants include ethoxylated nonyl phenols, alkyl arylpolyether alcohols, aliphatic polyether alcohols, alcohol ethoxysulfates and alkyl sulfonated diphenyl oxides. The most preferredsurfactant is ethoxylated nonyl phenol (with 15 EO). When used, thesurfactant is employed in an amount that aids the rate of dispersion ordissolution of the corrosion inhibitor composition into a concentratedcleaning solution. The surfactant preferably is employed in an amountthat is from about 0-10 percent-by-weight, and more preferably fromabout 3-7 percent-by-weight based on the final corrosion inhibitorcomposition.

The balance of these corrosion inhibitor compositions is comprised of asolubilizing alcohol, preferably the propylene glycol or propyleneglycol methyl ether solvent used in preparation of the quaternaryammonium salt, water and mixtures thereof. Known solubilizing alcoholsinclude the alkanols, alkanols, alkynols, glycols, polyols and mixturesthereof. While any of these conventional solubilizing alcohols may beemployed, in order to achieve the low hazard characteristics of thepresent invention, the solubilizing alcohol should be chosen from thepropylene glycols, propylene glycol ethers and mixtures thereof. Thealcohols improve the solubility of the components in the inhibitedcleaning solutions and also improve the handling properties of the finalcompositions. Examples of these properties include freezing point andrate of dispersion or dissolution into the cleaning solution. Apreferred embodiment of the present invention is a corrosion inhibitorcomposition containing at least one alcohol or its ether in an amountsufficient to prevent the corrosion inhibitor composition from freezingunder conditions of storage and use. Preferred solubilizing alcoholsinclude propylene glycol and dipropylene glycol methyl ether.

Corrosion inhibitors in accord with the foregoing composition arecharacterized by high flash points, i.e., flash points typically aboveabout 140° F., and reduced toxicity when compared to previously usedcompositions.

The foregoing corrosion inhibitor compositions are particularly usefulas components of aqueous cleaning solutions to retard and minimize thecorrosion of metal parts, particularly steel, being cleaned with thesesolutions. For the purpose of the present invention, the term “cleaningsolution” refers to an aqueous acidic or alkaline solution that isemployed in the cleaning of metal surfaces, e.g., the internal metalsurfaces of process equipment. These cleaning solutions typical have apH in the range of about 1 to about 10. Exemplary cleaning solutions andtheir uses are disclosed in several patents, e.g., U.S. Pat. Nos.3,413,160; 4,637,899; Re.30,796; and Re.30,714, all of which areincorporated herein by reference.

Cleaning solution compositions in accord with the present invention mayinclude at least one organic acid selected from the group consisting ofalkylene polyamine polycarboxylic acids, hydroxyacetic acid, formicacid, citric acid and mixtures or salts thereof together with acorrosion inhibitor in accord with the foregoing compositions present inan amount effective to inhibit the corrosion of metals in contact withthe solution. Exemplary organic acids include EDTA, tetraammonium EDTA,diammonium EDTA, HEDTA and salts thereof. These aqueous cleaningsolutions typically exhibit a pH from about 1 to about 10. Exemplaryamounts of corrosion inhibitor are from about 0.05 to about 1percent-by-weight wherein the quaternary ammonium salt is present in anamount from about 5 to about 50 percent-by-weight of the inhibitor.Exemplary organic acid cleaning solutions and typical pHs. are shown inTable 1.

TABLE 1 Typical Organic Acid Cleaning Solutions Active Agent(s) pHHEDTA¹ 2.3 diammonium EDTA² 5 tetraamonium EDTA² 9.2 tetraamonium EDTAand citric acid 5 tetraamonium EDTA and formic acid 5 hydroxyacetic andformic acids 2.2 trisodium salt of B + H₂SO₄ 1.2-1.5 ¹HEDTA isN-2-hydroxyethyl N,N′,N′-ethylene diamine triacetic acid. ²EDTA isN,N,N′,N′-ethylene diamine tetracetic acid.

The corrosion inhibitor compositions of the present invention may alsobe used in aqueous cleaning solutions to inhibit the corrosion of metalby a variety of inorganic acids, e.g., sulfuric acid, hydrochloric acidand phosphoric acid. These cleaning solutions include an amount ofcorrosion inhibitor in accord with the present invention that issufficient to inhibit the corrosion of metals by these inorganic acids.Exemplary amounts of corrosion inhibitor are from about 0.05 to about 1percent-by-weight wherein the quaternary ammonium salt is present in anamount from about 5 to about 50 percent-by-weight of the inhibitor.

Corrosion inhibitors in accord with the present invention prevent, or atleast minimize, excess corrosion of clean base metal during chemicalcleaning operations. The corrosion inhibitor compositions may beemployed advantageously over a wide pH range in a wide number ofcleaning solutions employing an organic acid as the cleaning agent.

Cleaning solutions are employed predominantly in the removal of scaleand rust from ferrous metals. However, the solutions often contact othermetals that are present as an integral part of the system being cleaned.Examples of those metals include copper, copper alloys, zinc, zincalloys and the like.

The corrosion inhibitor compositions of the present inventionadvantageously are employed in an amount sufficient to inhibitacid-induced corrosion of metals that are in contact or contacted withaqueous cleaning solutions. Typically, the corrosion inhibitorcompositions of the present invention are employed in an amountsufficient to give a corrosion rate less than or equal to about 0.015lb/ft²/day. Preferably, from about 145-2900 mg/l of corrosion inhibitor,measured as the sum of the quaternary ammonium salt and thesulfur-containing compound, are employed in the cleaning solution, basedon the total volume of the final inhibited cleaning solution.Preferably, the amount of the quaternary ammonium salt employed rangesfrom about 120-2400 mg/l, and the amount of sulfur-containing compoundthat is employed ranges from about 25-500 mg/l. The amount of corrosioninhibitor composition employed is dependent upon the composition of thespecific cleaning solution to be inhibited. For example, the presence ofhydroxy ethyl ethylene diamine triacetic acid requires a relativelylarge amount of corrosion inhibitor composition. Preferably, thecorrosion inhibitor composition is dissolved or dispersed in thecleaning solution prior to contacting the cleaning solution and themetal to be cleaned.

The following examples and comparative examples are merely illustrativeof the present invention. These examples should not be construed aslimiting in scope. All parts and percentages are by weight unlessotherwise specified.

Preparation of Dodecyl Pyridinium Bromide

Dodecyl pyridinium bromide (DDPB) was prepared in a stirred three neckflask (250 ml) fitted with a reflux condenser and a type j thermocoupleprobe. Heat was supplied by a Glascol mantel controlled with an IR²digital temperature controller. In each test, 64.2 grams of alcohol,glycol or glycol ether, 20.7 grams of pyridine (0.26 mole) and 65.1grams (0.26 mole) of 1-bromo dodecane were placed in the flask. Theflask was heated with stirring to 85° C. An exotherm was encounteredwhich caused the temperature to rise to about 100° C. The temperaturecontroller was adjusted to 95° C. and this temperature was maintainedthroughout the preparation. At set times, samples were drawn and thebromide concentration was determined on a Mettler Model 25 autotitratorusing the chloride specific ion silver nitrate method. The reaction wasterminated when the bromide concentration reached 96% of the theoreticalvalue.

Where dipropylene glycol methyl ether (DPM) and tripropylene glycolmethyl ether (TPM) were used as solvents, it was necessary to add 10 mlof water at the six-hour time mark to drive the reaction to completion.The concentration of DDPB in isopropyl alcohol, propylene glycol andpropylene glycol methyl ether was 57 percent-by-weight while theconcentration in DPM and TPM was 54 percent-by-weight. FIG. 1illustrates the rates and percent completion of these preparations. Allof the preparations reached at least 95% completion in about eight hoursat 95° C. The comparative preparation in isopropyl alcohol took thelongest to reach completion. The three preparations in glycol etherswere essentially equivalent, while the preparation in propylene glycolwas the fastest of the five reactions. It must be noted that thepreparations in DPM and TPM required the addition of water to force thereaction to proceed to greater than 95% completion.

Because of the exothermic nature of the reaction, it may be necessary toadd the second compound, 1-bromododecane, slowly or incrementally duringthe reaction process.

Cleaning Solutions

Cleaning solutions inhibited with corrosion inhibitors prepared inaccord with the present invention were prepared, tested and comparedwith a conventional corrosion inhibitor (A251) prepared in accord withthe disclosure in the '899 patent. Corrosion inhibitors were preparedfor use with the following organic acid cleaning solutions:

TABLE 2 Cleaning Solutions Cleaning Solution Active Agent(s) 10% Sol A4% tetraammonium EDTA 10% Sol B 4% diammonium EDTA  3% Sol C 3%hydroxyacetic acid and formic acid  2% Sol D 2% formic acid and citricacid 10% Sol E 4% trisodium HEDTA (sulfuric acid to pH 1.4)

Test Specimens

Carbon steel specimens (1018 CS) were purchased from Corrosion TestSupplies, Inc. of French Settlement, La.

Rings for conducting scale solution tests were obtained fromPennsylvania Electric Co. The boiler from which the tubes were removedwas a Combustion Engineering combined circulation boiler. From thechemical analysis the tubes were determined to be SA-213-T22 alloy steel(2.25% Cr). These tubes are later referenced as the Pen-II tubes.

Carbon steel tube sections from Georgia Power Co. at Milledgeville, Ga.,having scale containing both magnetite and copper were obtained forother tests.

Finally, carbon steel tubes from the city of Hamilton, Ohio, were alsotested. These tubes included a heavy scale deposit having 37% iron and24% copper deposited at the rate of 20 g/ft².

Static Corrosion Tests

Static corrosion tests were conducted using conventional pressure bombs.For each test, a single 1018 CS coupon having a surface area of 36.22cm² was weighed and placed in the glass bomb liner with 90 ml of solvent(s/v=0.4 cm⁻¹) inhibited with 0.1% of the test formulation. The lineralso contained a Teflon cylinder to reduce the solvent volume. The bombswere closed and placed in an oil bath that had been raised to the testtemperature. After 24 hours at the test temperature the test couponswere removed, cleaned and re-weighed.

Iron Oxide Scale Dissolution Tests

Iron oxide scale dissolution was determined from the followingprocedure. Rings were cut from the Pen-II tubes and machined to aconstant surface area of 50 cm². For each test, three of the rings wereplaced in 250 ml of inhibited solvent in a stirred titanium Parr bombfor 24 hours at the test temperature. Samples were periodically removedand the iron concentration determined using a Perkin-Elmer inductivelycoupled plasma spectrometer. It was presumed that the cleaning plateauindicated that the surfaces were cleaned. A corrosion rate for the timeperiod following the plateau was calculated from the change in ironconcentration between the plateau and the end of the tests.

Copper Removal Tests

The removal of iron oxide and copper from utility power boilers is oftenaccomplished using a two step procedure employing tetraammonium EDTA.Iron oxide is dissolved under reducing conditions at a temperature up toabout 300° F. The temperature is then lowered to about 150° F. and anoxidant, e.g., oxygen, air or hydrogen peroxide, introduced to oxidizeferrous EDTA to ferric EDTA. This chemical then passivates the steel andoxidizes any copper that plated onto the steel during the iron removalstage. It is critical that an inhibitor protect steel during the ironremoval stage but not interfere with passivation and copper removalduring the copper removal stage.

To test the effect of inhibitors prepared in accord with the presentinvention on copper removal, the following simulation was used. Aconcentrate of ferrous EDTA was produced by heating 25% Sol A cleaningsolution with iron powder. Two 1018 CS coupons were heated for 24 hoursat 300° F. in 400 ml of a solution containing ferrous EDTA (about 4,000ppm iron), sufficient cupric acetate to give about 500 ppm copper, freeEDTA (about 2%) and about 0.2% inhibitor. This portion of the testsimulated the iron removal stage and plating of copper.

After 24 hours the solutions were sampled to determine iron and copperconcentrations using the Perkin-Elmer inductively coupled plasmaspectrometer and free EDTA by the copper specific ion electrode method.The pH was adjusted to 9.3 with ammonium hydroxide, the free EDTAcleaning solution adjusted to 2% and the solvent and coupons placed inthe test cell. The solutions containing the copper plated coupons wereheated to 150° F. Air was passed through the solutions at 700 ml/min andthe pH values and EMF (Pt vs. S.C.E.) were measured for three hours.Foam was controlled by adding conventional anti-foaming agents. Thesolution was sampled periodically to determine iron and copperconcentrations and the pH was maintained at 8.7 at 150° F.,corresponding to a pH of 9.2 at 75° F. After three to four hours ofexposure to the oxidizing solution, the coupons were removed andexamined.

In another experiment, the ferrous EDTA was oxidized using 30% hydrogenperoxide (M240) and circulated over the copper plated coupons at 350ml/min for a total of four hours. The pH was maintained at 8.7 in situ(corresponding to a pH of 9.2 at 75° F.) with ammonium hydroxide and theEMF maintained at greater than −100 mv (vs. S.C.E.) by periodic additionof 30% hydrogen peroxide.

In a final experiment to better quantify the effects of the inhibitor oncopper removal, the steel coupons were treated with the concentratedferrous EDTA solution described above, but modified to contain 3% freeEDTA, for 24 hours at 300° F. After this exposure, the solution wascooled to 150° F. and 10 ml of 30% hydrogen peroxide introduced, alongwith 2 ml of ammonium hydroxide. The solution was stirred at 80 rpm for5 hours, during which the concentrations of iron and copper weremeasured at various times.

Static Corrosion Rates

Static corrosion rates were determined for three inhibitor formulationsprepared with dodecyl pyridinium bromide prepared in accord with thepresent invention and compared with the corrosion rates observed forsimilar inhibitors prepared using isopropyl alcohol. These formulationswere prepared to contain 42% of the reaction mixture of the DDPB/solventpreparation, 5% ammonium thiocyanate, 5% nonyl phenol (15 EO) surfactantand 48% water. A concentration of 0.1% volume was used to inhibit Sol Aat 300° F. and Sol B at 200° F. All of these formulations were found tobe effective inhibitors of corrosion of 1018 CS coupons under the testconditions. The results are reported in Table 3.

TABLE 3 Corrosion Rates of DDPB/NH₄SCN Mixes for 1018 CS with 0.1% Inh.Sol A Sol B Corrosion Rate Corrosion Rate Alcohol in Mix (lb/ft²/day)(lb/ft²/day) A251 0.0015 0.0035 2-Propanol 0.0018 0.0032 PM 0.00140.0032 DPM 0.0018 0.0032 TPM 0.0014 0.0035

Formulations with a variety of concentrations of the DDPB/DPM solventpreparation, sulfur-containing compound (ammonium thiocyanate) andnonionic surfactant (nonyl phenol with 15 EO) were prepared. Thecorrosion rates in Sol A inhibited with 0.1% of these formulations weredetermined. These results are reported in Table 4 below.

TABLE 4 DDPB/DPM Mix Optimization Nonyl Phenol Sol A DDPB/DPM (15 EO)HN₄SCN Corrosion Rate (%) (%) (%) (lb/ft²/day) 40.00 5.000 2.000 0.0014040.00 2.500 5.000 0.00170 50.00 2.500 2.000 0.00180 30.00 2.500 2.0000.00150 30.00 2.500 8.000 0.00140 50.00 2.500 8.000 0.00180 40.00 0.0002.000 0.00260 40.00 0.000 8.000 0.00240 30.00 5.000 5.000 0.00120 30.000.000 5.000 0.00340 50.00 0.000 5.000 0.00280 40.00 5.000 8.000 0.0014040.00 2.500 5.000 0.00130 40.00 2.500 5.000 0.00170 50.00 5.000 5.0000.00120 45.00 5.000 5.000 0.00140  0.00 0.000 0.000 0.02400 30.00 2.5001.000 0.00350 20.00 2.500 5.000 0.00170 20.00 2.500 2.500 0.00180 Theremainder of each formulation is water

Table 4 seems to indicate that the corrosion rates are reduced not onlyby DDPB and ammonium thiocyanate, but also by the surfactant. This datasuggests that corrosion inhibition is a complex process which may beimproved by selection of the nonionic surfactant.

Additional formulations were prepared using different solvent's whereinthe concentration of the DDPB/solvent mixture was maintained at 40percent. These formulations included 2% ammonium thiocyanate 7and 2.5 to5% surfactant. Formulations and corrosion rates are shown in Table 5.

TABLE 5 Properties of DDPB/Alcohol or Glycol Mixes DDPB/ CorrosionCorrosion Solvent NH₄SCN Water Solvent Surfactant IPA Rate RateFormulation (%) (%) (%) (%) (%) (%) Sol A Sol B 18-22-27 40 2 0 55, PG2.5 0 0.0019 0.0032 18-22-29 40 2 27.5 0 2.5 27.5 0.0019 0.0030 18-23-2340 2 13.5 41.5, DPM 2.5 0 0.0019 0.0018 18-23-33 40 2 13.5 39.5, DPM 5.00 0.0013 0.0032 Corrosion rate is lb/ft²/day.

The results of copper removal tests for these formulations are reportedin Table 6.

TABLE 6 Copper Removal Data Inhibitor/ Copper Anti- Conc. Remain-foaming Inh. Test Time ing Agent (%) Oxidizer Condition Hrs (%) A251/M450.2 Air 700 3 10 ml/min 18-23-33/M45 0.2 Air 700 3 80 ml/min 18-23-33/0.2 Air 700 4  0 M246 ml/min A251 0.2 Peroxide Pump 350 4 20 ml/min18-23-33 0.2 Peroxide Pump 350 4 70 ml/min A251 0.2 Peroxide Stirred 805 25 rpm 18-23-33 0.1 Peroxide Stirred 80 5 70 rpm 18-23-33 0.2 PeroxideStirred 80 5 80 rpm

Additional tests were conducted with corrosion inhibitor 18-23-33. Theseincluded iron oxide scale dissolution tests conducted in the cleaningsolutions and using the method described above. FIGS. 2-6 illustrate theresults of these tests. Each figure compares the results observed with acleaning solution including a corrosion inhibitor prepared in accordwith the present invention (formulation 18-23-33) to results of aformulation prepared in accord with the '899 patent (A251). The curvesin FIGS. 2-4 are virtually identical, thus establishing that the lowhazard corrosion inhibitor of the present invention provides resultsessentially identical to the results of the more hazardous conventionalinhibitors. While it would appear from FIG. 5 that the corrosioninhibitor of the present invention is not as effective as theconventional solution in Sol C cleaning solution, FIG. 6 indicates thatthe inhibitor of the present invention is better than the priorinhibitor when used with Sol E cleaning solutions.

The post plateau corrosion rates for each of the cleaning solutionsillustrated in FIGS. 2-6 are compared in FIG. 7. It is obvious from FIG.7 that all of these solutions provide acceptable corrosion rates of lessthan 0.015 lb/ft/²/day.

The results of copper removal tests in accord with the previouslydescribed method are illustrated in FIGS. 8-10. These tests compare theresults of corrosion inhibitor 18-23-33 with the conventional A251inhibitor. Air blow tests are illustrated in FIG. 8. The solutionsinitially contained 6000 ppm iron. After three hours about 80% of thecopper had been removed from the solution inhibited with A251 while onlyabout 30% of the copper had been removed from the solution inhibitedwith 18-23-33. Both solutions included a conventional, siliconeanti-foaming agent (M45). When another conventional, alcoholanti-foaming agent (M246), was substituted in the formulation with18-23-33, copper removal was significantly improved. About 90% removalwas achieved after three hours with removal substantially complete atfour hours. Because the iron concentrations remained substantiallyconstant, it may be assumed that corrosion of the steel coupon wasinsignificant.

FIGS. 9 and 10 illustrate additional results using hydrogen peroxide asthe oxidizer.

Additional copper removal tests were conducted in Sol A cleaningsolution. A copper solvent was synthesized containing ferrous EDTA, freeEDTA and enough hydrogen peroxide to oxidize all of the iron to theferric state. The solvent contained 554 g ferrous EDTA (1.8% iron), 80 gSol A, 1365 g water and 40 g 30% hydrogen peroxide. A weighed coppercoupon having a surface area of 37.8 cm² was placed into 100 ml of thiscopper solvent along with a test amount of inhibitor, typically 0.2% ina stainless steel test bomb. The temperature was maintained at 160° F.for six hours, after which the copper coupon was retrieved, dried andweighed.

The effect of the inhibitor on copper removal from steel was alsotested. Four 1018 CS coupons with 36 cm² surface area were heated in astirred Parr bomb for 24 hours at 350° F. in a solution containingferrous EDTA (4000 ppm iron), sufficient cupric acetate to give about500 ppm copper, free EDTA and 0.2% inhibitor. The solution was preparedfrom the following components: 55 ml ferrous EDTA (1.8% iron), 100 ml10% Sol A, 0.34 g cupric acetate, 100 ml water and 0.5 ml inhibitor(0.2%). This part of the test was designed to simulate the iron removalstage and the plating of copper. After 24 hours the solutions werecooled to the test temperature and sampled to determine iron and copperconcentration. An additional 2 ml of the Sol A and 6% ml of 30% hydrogenperoxide were injected and the solution stirred at 80 rpm for theduration of the test. The tests were sampled periodically to determinethe concentrations of iron and copper. At the end of the tests thecoupons were examined for the presence of residual iron and the solventwas filtered through a 0.45 micron filter.

Tests to determine the ability to remove copper were conducted onseveral corrosion inhibitor formulations using a variety ofsulfur-containing compounds.

TABLE 7 Corrosion Inhibitor Formulations with Different Sulfur CompoundsSurfac- Formu- DDPB DPM tant Water Sulfur lation (%) (%) (%) (%) (%)Compound 20-16-35 21 52 4.5 17.5 5 diethyl thiourea 20-28-12 21 50 5 175 diethyl thiourea 2 ammonium thiocyanate 20-48-23 20 52 5 16 5mercaptoacetic- acid 20-65-4 21 16 5 38 20 25% Na₂CS₃

The results of the replicant at temperatures of 150° F., 130° F. and110° F. are illustrated in FIGS. 11-13. All of the tested inhibitorsallow the solvent to completely remove any plated copper in six hours at150° F. At 130° F., at least 90% of the copper was removed. Even at 110°F., satisfactory copper removal was achieved with superior results beingshown with the formulation using the mercaptoacetic acid.

Static corrosion rates for these formulations in the five solvents aresummarized in the following table:

TABLE 8 Static Corrosion Rates Sol A¹ Sol B² Sol C² Sol D² Sol E³Formulation lb/ft²/day lb/ft²/day lb/ft₂/day lb/ft²/day lb/ft²/day A2510.0014 0.0036 0.0025 0.0025 0.0014 A224 0.0055 0.0031 0.0022 0.0022 NA18-23-33 0.0013 0.0031 0.0020 0.0021 0.0012 20-16-35 0.0040 0.00300.0017 0.0025 NA 20-28-12 0.0025 0.0021 0.0021 0.0011 20-48-23 0.00240.0015 0.0030 0.0023 0.0015 20-65-4 0.0023 0.0010 0.0020 0.0026 NA ¹1010CS, 0.1% Inh, 300° F., s/v = 0.35 cm⁻¹ ²1010 CS, 0.1% Inh, 200° F., s/v= 0.35 cm⁻¹ ³1010 CS, 0.1% Inh, 150° F., s/v = 0.35 cm⁻¹

All of the inhibitor formulations tested provide superior staticcorrosion results.

In order to study the effect of different sulfur-containing compounds onthe corrosion rate when used with inhibitor formulations in accord withthe present invention, several test formulations were prepared. Testformulations using DDPB prepared in DPM and further including water, asurfactant (nonyl phenol with I5 EO) and one or more sulfur-containingcompounds were prepared. Sulfur-containing compounds tested includediethyl thiourea, ammonium thiocyanate and mercaptoacetic acid. Thecomposition of these formulations is summarized in Table 9.

TABLE 9 Test Formulations DDPB/ Surfactant Sulfur DPM DPM Water NP (15EO) Compounds Deodorant Flash Point Formulation (%) (%) (%) (%) (%) (%)(° F.) 20-28-12 40 34 14 5 diethyl 0 >200 thiourea-5 ammoniumthiocyanate-2 20-48-23 39 34 16 5 mercapto- 0 >200 acetic acid-626-77-26 40 24 24 5 diethyl 0 >200 thiourea-5 ammonium thiocyanate-220-78-9 40 25 24 5 mercapto- 0 >200 acetic acid-6 25-04-32 40 24 24 5mercapto- 1 >200 acetic acid-6

These formulations were employed in a series of static corrosion testsconducted in accord with the procedure described :above. The results ofthese tests are reported in Tables 10 and 11.

TABLE 10 Static Corrosion Test with 0.2% 20-77-26 Inh. 10% Sol A 10% SolB 3% Sol C 2% Sol D 10% Sol E Metal 300° F. 200° F. 200° F. 200° F. 150°F. 1018 CS 0.0032 0.0044 0.0020 0.0020 0.0010 SA-213-T11 0.0027 0.00340.0021 0.0018 0.0014 SA-213-T22 0.0031 0.0037 0.0022 0.0020 0.0030SA-209T1a 0.0028 0.0023 0.0019 0.0020 0.0090 515 Gr70 0.0020 0.00310.0020 0.0020 0.0099 s/v 0.6 cm⁻¹; all corrosion rates are lb/ft²/day.

TABLE 11 Static Corrosion Test with 0.2% 20-78-9 Inh. 10% Sol A 10% SolB 3% Sol C 2% Sol D 10% Sol E Metal 300° F. 200° F. 200° F. 200° F. 150°F. 1018 CS 0.0022 0.0040 0.0018 0.0026 0.0010 SA-213-T11 0.0010 0.00370.0036 0.0028 0.0015 SA-213-T22 0.0020 0.0018 0.0032 0.0040 0.0025SA-209T1a 0.0021 0.0040 0.0027 0.0030 0.0013 515 Gr70 0.0013 0.00380.0020 0.0022 0.0013 s/v 0.6 cm⁻¹; all corrosion rates are lb/ft²/day.

The inhibitors tested provided satisfactory results in all of thesolvents.

Because of the strong sulfur odor associated with mercaptoacetic acid,it may be desirable to employ a masking agent or deodorant to reduce theoffensive odor. One exemplary agent is lemon oil.

Scale dissolution tests were conducted in accord with the proceduredescribed above. Tests were conducted on the Pen-II tubes having a scalecomprised mostly of magnetite, on the Georgia Power tubes with magnetiteand copper scale and on the Hamilton tubes with heavy iron/copper scale.

The results of the tests on the Pen-II tubes are illustrated in FIGS.14-17. The tested solutions cleaned 100% of the scale in less than 24hours and provided adequate corrosion protection. However, because ofhigher than expected corrosion rates in Sol E, it was determined thatthe concentration of inhibitor should be increased to 0.3% in thissolution.

The Georgia Power tubes were fouled with both iron oxide and copperdeposits. The previously described process for removing both iron oxideand copper was applied to these tubes. The results of the iron removalstep are illustrated in FIG. 18. Using the iron solution generated inthis step, copper removal was accomplished by lowering the temperatureto 150° F. and injecting 30% hydrogen peroxide into the bomb. Copperremoval results are illustrated in FIG. 19. There were no significantdifferences in the rate of copper removal. FIG. 20 compares the rate ofcopper removal at 150° F. with that at 110° F. While inhibitor 25-4-32would permit copper removal at lower temperatures, all three testedinhibitors showed satisfactory results.

Shelf-life tests were conducted by exposing the inhibitor formulationsto storage for 180 days at both room temperature and 110° F. At theconclusion of storage under these conditions, inhibitor solutions wereused in static corrosion tests. The results of these tests are reportedin Tables 12-17. No loss of inhibitor quality was seen.

TABLE 12 Static Corrosion Test with 0.2% 20-77-26 Inh. 120-Day ShelfLife Test Storage 10% Sol A 10% Sol B 3% Sol C Metal Temp ° F. 300° F.200° F. 200° F. 1018 CS 72 0.0020 0.0036 0.0013 1018 CS 110 0.00300.0030 0.0022 SA-213-T11 72 0.0016 0.0027 0.0025 SA-213-T11 110 0.00200.0012 0.0013 s/v 0.6 cm⁻¹; all corrosion rates are lb/ft²/day.

TABLE 13 Static Corrosion Tests with 0.2% 20-78-9 Inh. 120-Day ShelfLife Test Storage 10% Sol A 10% Sol B 3% Sol C Metal Temp ° F. 300° F.200° F. 200° F. 1018 CS 72 0.0020 0.0030 0.0020 1018 CS 110 0.00200.0035 0.0017 SA-213-T11 72 0.0015 0.0015 0.0018 SA-213-T1l 110 0.00150.0028 0.0031 s/v 0.6 cm⁻¹; all corrosion rates are lb/ft²/day.

TABLE 14 Static Corrosion Tests with 0.2% 20-78-9 Inh. 120-Day ShelfLife Test Storage 10% Sol A 10% Sol B 3% Sol C Metal Temp ° F. 300° F.200° F. 200° F. 1018 CS 72 0.0026 0.0020 0.0018 1018 CS 110 0.00180.0025 0.0021 SA-213-T11 72 0.0020 0.0017 0.0022 SA-213-T11 110 0.00140.0010 0.0024 s/v 0.6 cm⁻¹; all corrosion rates are lb/ft²/day.

TABLE 15 Static Corrosion Tests with 0.2% 20-77-26 Inh. 120-Day ShelfLife Test Storage 10% Sol A 10% Sol B 3% Sol C Metal Temp ° F. 300° F.200° F. 200° F. 1018 CS 72 0.0028 0.0038 0.0017 1018 CS 110 0.00260.0035 0.0017 SA-213-T11 72 0.0012 0.0010 0.0015 SA-213-T11 110 0.00180.0020 0.0015 s/v 0.6 cm⁻¹; all corrosion rates are lb/ft²/day.

TABLE 16 Static Corrosion Tests with 0.2% 20-78-9 Inh. 120-Day ShelfLife Test Storage 10% Sol A 10% Sol B 3% Sol C Metal Temp ° F. 300° F.200° F. 200° F. 1018 CS 72 0.0030 0.0039 0.0018 1018 CS 110 0.00180.0040 0.0016 SA-213-T11 72 0.0011 0.0010 0.0023 SA-213-T11 110 0.01100.0024 0.0026 s/v 0.6 cm⁻¹; all corrosion rates are lb/ft²/day.

TABLE 17 Static Corrosion Tests with 0.2% 25-4-32 Inh. 120-Day ShelfLife Test Storage 10% Sol A 10% Sol B 3% Sol C Metal Temp ° F. 300° F.200° F. 200° F. 1018 CS 72 0.0020 0.0040 0.0016 1018 CS 110 0.00200.0038 0.0020 SA-213-T11 72 0.0016 0.0010 0.0026 SA-213-T11 110 0.00180.0010 0.0029 s/v 0.6 cm⁻¹; all corrosion rates are lb/ft²/day.

In order to test the stored corrosion inhibitors of the presentinvention with scale including high copper content, boiler tube samplesfrom a unit in the city of Hamilton, Ohio, were tested. The scale onthese tubes contained 24% copper. These tubes were cleaned to removeiron oxide and copper. Iron dissolution and copper removal curves areshown in FIGS. 21 and 22. Satisfactory results were observed.

The effect of the ratio of DDPB to DPM in the quaternary ammonium saltpreparation was examined by varying the weight ratio of DDPB to DPM from0.5:1 to 1.5:1. The effect of temperature on the reaction rate was alsoexamined at 200° F. and 230° F. The results of these tests areillustrated in FIG. 23. From these tests it appears that it ispreferable to conduct the reaction at the higher temperature and weightratio of quaternary salt to solvent.

While DDPB is the preferred quaternary ammonium salt, four alternatesalts were prepared. In two preparations, chloro methyl naphthalene wasreacted with, respectively, quinoline and pyridine. In anotherpreparation, dodecyl bromide was reacted with quinoline. In the finalpreparation, dodecyl chloride was reacted with pyridine. The ratesobserved in these reactions are illustrated in FIG. 24. The results ofthese tests show that bromide is a better leaving group than chlorideand that a halide bonded to a carbon atom conjugated to an aromatic ringappears to be a better leaving group than a halide attached to carbonnext to another aliphatic carbon. These examples confirm that pyridineis a better nucleophile than quinoline in this reaction.

Field Test

In order to confirm the successful performance of the corrosioninhibitors of the present invention in an actual industrial setting, apilot plant preparation and field test was arranged. Initially, aquantity of dodecyl pyridinium bromide (DDPB) was prepared in accordwith the present invention using dipropylene glycol methyl ether (DPM)as the solvent. A reaction vessel containing 268 lb DPM, 87 lb pyridineand 137 lb dodecyl bromide was heated to about 185° F. to initiate thereaction. After about 1 hour at temperature, an additional 136 lbdodecyl bromide was added and the temperature raised to about 230° F.The vessel was sampled hourly and the progress of the reaction followedby monitoring the bromide concentration using a silver nitrateautotitrator. After 4 hours at temperature, 47 lb water was added. After6 hours, the temperature was raised to 240° F. At 7.5 hours, the reactorwas cooled below 150° F., 402 lb of DPM was added. The mixture then wasallowed to stand for about 16 hours.

The reaction coordinate, temperatures and pressures measured during thispreparation are illustrated in FIG. 25. The loss of temperature after 1hour was due to the injection of the second portion of DPM. The reactionappeared to be complete after 5 hours following injection of water atthe 4-hour mark. The reaction was terminated at 7.5 hours by addition ofthe remainder of the DPM. The initial pressure in the reactor wasprobably due to unreacted pyridine. While the DDB was added in twobatches in this preparation, it may all be added initially, if desired.

A corrosion inhibitor composition was prepared from the foregoingmixture by adding 430 lb water, 84 lb nonionic surfactant (nonyl phenolwith 15 EO) and 100 lb mercaptoacetic acid with stirring at 100° F. Ifdesired, a deodorant such as lemon oil may be included. In thisinstance, 16 lb of lemon oil was added. The pH of the final solution wasabout 1.8. The pH may be increased, if desired, e.g., by addition of0.1% monoethanolamine (MEA).

A series of static corrosion tests were conducted in accord with thepreviously described procedure using 24-hour tests at s/v ratios of 0.6cm⁻¹ and 1.0 cm⁻¹. The test results are reported in Tables 18-25. Ingeneral, an inhibitor loading of 0.2% was satisfactory for all metalsand all s/v ratios.

TABLE 18 Static Corrosion Rates for Field Test Inhibitor in Sol A at300° F. Conc. Sol A Inhibitor Rate (%) s/v, cm⁻¹ (%) Metal lb/ft²/day 100.6 0.1 AISI 1018 0.0013 10 0.6 0.2 AISI 1018 0.0014 10 0.6 0.1 SA 515gr 70 0.0010 10 0.6 0.2 SA 515 gr 70 0.0011 10 0.6 0.2 SA 209T1a 0.001010 0.6 0.2 SA 213T11 0.0014 10 0.6 0.2 SA 213T22 0.0020 10 1.0 0.2 AISI1018 0.0011 10 1.0 0.2 SA 515 gr 70 0.0011 10 1.0 0.2 SA 209T1a 0.001310 1.0 0.2 SA 213T11 0.0013 10 1.0 0.3 SA 213T11 0.0011 10 1.0 0.2 SA213T22 0.0016 10 1.0 0.3 SA 213T22 0.0014 20 1.0 0.2 SA 515 gr 70 0.001020 1.0 0.2 SA 209T1a 0.0053 20 1.0 0.2 SA 213T22 0.0031

TABLE 19 Static Corrosion Rates for Field Test Inhibitor in Sol B at200° F. Conc. Sol B Inhibitor Rate (%) s/v, cm⁻¹ (%) Metal lb/ft²/day 100.6 0.1 AISI 1018 0.0022 10 0.6 0.2 AISI 1018 0.0021 10 0.6 0.1 SA 515gr 70 0.0020 10 0.6 0.2 SA 515 gr 70 0.0021 10 0.6 0.2 SA 209T1a 0.001010 0.6 0.2 SA 213T11 0.0021 10 0.6 0.2 SA 213T22 0.0010 10 1.0 0.2 AISI1018 0.0020 10 1.0 0.2 SA 515 gr 70 0.0019 10 1.0 0.2 SA 209T1a 0.001010 1.0 0.2 SA 213T11 0.0020 10 1.0 0.2 SA 213T22 0.0010 10 1.0 0.3 SA213T11 0.0019 10 1.0 0.3 SA 213T22 0.0010 20 1.0 0.2 SA 515 gr 70 0.001420 1.0 0.2 SA 209T1a 0.0010 20 1.0 0.2 SA 213T22 0.0010

TABLE 20 Static Corrosion Rates for Field Test Inhibitor in Sol C at200° F. Conc. Sol C Inhibitor Rate (%) s/v, cm⁻¹ (%) Metal lb/ft²/day 31.0 0.2 AISI 1018 0.0015 3 1.0 0.2 SA 515 gr 70 0.0014 3 1.0 0.2 SA209T1a 0.0027 3 1.0 0.2 SA 213T11 0.0024 3 1.0 0.2 SA 213T22 0.0030 61.0 0.2 AISI 1018 0.0012 6 1.0 0.2 SA 515 gr 70 0.0015 6 1.0 0.2 SA209T1a 0.0045 6 1.0 0.2 SA 213T11 0.0027* 6 1.0 0.2 SA 213T22 0.0039*3/0.25% Y1 1.0 0.2 SA 213T11 0.0026* 3/0.25% Y1 1.0 0.2 SA 213T220.0026* *Very slight pit

TABLE 21 Static Corrosion Rates for Field Test Inhibitor in Sol D at200° F. Conc. Sol D Inhibitor Rate (%) s/v, cm⁻¹ (%) Metal lb/ft²/day 21.0 0.2 AISI 1018 0.0020 2 1.0 0.2 SA 515 gr 70 0.0014 2 1.0 0.2 SA209T1a 0.0026 2 1.0 0.2 SA 213T11 0.0022 2 1.0 0.2 SA 213T22 0.0033 41.0 0.2 AISI 1018 0.0022 4 1.0 0.2 SA 515 gr 70 0.0019 4 1.0 0.2 SA209T1a 0.0038 4 1.0 0.2 SA 213T11 0.0028 4 1.0 0.2 SA 213T22 0.012** 41.0 0.3 SA 213T22 0.0028 4/0.25% Y1 1.0 0.2 SA 213T11 0.0028 4/0.25% Y11.0 0.2 SA 213T22 0.0030* *Very slight pit **Deep pits

TABLE 22 Static Corrosion Rates for Field Test Inhibitor in Sol E at150° F. Conc. Sol E Inhibitor Rate (%) s/v, cm⁻¹ (%) Metal lb/ft²/day 100.6 0.1 AISI 1018 0.0015 10 0.6 0.2 AISI 1018 0.0014 10 0.6 0.1 SA 515gr 70 0.0019 10 0.6 0.2 SA 515 gr 70 0.0014 10 0.6 0.2 SA 209T1a 0.003310 0.6 0.2 SA 213T11 0.0037 10 0.6 0.2 SA 213T22 0.0034 10 1.0 0.2 AISI1018 0.0013 10 1.0 0.2 SA 515 gr 70 0.0013 10 1.0 0.2 SA 209T1a 0.002910 1.0 0.2 SA 213T11 0.0032 10 1.0 0.2 SA 213T22 0.0025

TABLE 23 Static Corrosion Rates for Field Test Inhibitor in AmmoniumCitrate, pH 3.5 at 200° F. Conc. Citrate Inhibitor Rate (%) s/v, cm⁻¹(%) Metal lb/ft²/day 3 0.6 0.1 AISI 1018 0.0024 3 0.6 0.2 AISI 10180.0017 3 0.6 0.1 SA 515 gr 70 0.0017 3 0.6 0.2 SA 515 gr 70 0.0020 3 0.60.2 SA 209T1a 0.0031 3 0.6 0.2 SA 213T11 0.0011 3 0.6 0.2 SA 213T220.0019 3 1.0 0.2 AISI 1018 0.0014 3 1.0 0.2 SA 515 gr 70 0.0015 3 1.00.2 SA 209T1a 0.0025 3 1.0 0.2 SA 213T11 0.0011 3 1.0 0.2 SA 213T220.0015

TABLE 24 Static Corrosion Rates for Field Test Inhibitor in AmmoniumCitrate, pH 6.5 at 300° F. Conc. Citrate Inhibitor Rate (%) s/v, cm⁻¹(%) Metal lb/ft²/day 3 0.6 0.2 AISI 1018 0.0018 3 0.6 0.2 SA 515 gr 700.0018 3 0.6 0.2 SA 209T1a 0.0015 3 0.6 0.2 SA 213T11 0.0021 3 0.6 0.2SA 213T22 0.0027 3 1.0 0.2 AISI 1018 0.0019 3 1.0 0.2 SA 515 gr 700.0013 3 1.0 0.2 SA 209T1a 0.0018 3 1.0 0.2 SA 213T11 0.0021 3 1.0 0.2SA 213T22 0.0034

TABLE 25 Static Corrosion Rates for Field Test Inhibitor in Misc.Solvents at 150° F. Conc., Acid Inhibitor Rate (%) s/v, cm⁻¹ (%) Metallb/ft²/day 10% Sulfuric 0.6 0.2 AISI 1018 0.0015 10% Sulfuric 0.6 0.2 SA515 gr 70 0.0025 15% Sulfuric 0.6 0.2 AISI 1018 0.0017 15% Sulfuric 0.60.2 SA 515 gr 70 0.0043  7.5% HSSR* 0.6 0.2 AISI 1018 0.0010 7.5% HSSR0.6 0.2 SA 515 gr 70 0.0018  15% HSSR 0.6 0.2 AISI 1018 0.0069  15% HSSR0.6 0.2 SA 515 gr 70 0.0058 7.5% HSSR 0.6 0.3 410 0.0180 10% Sulfamic0.6 0.2 AISI 1018 0.0013 10% Sulfamic 0.6 0.2 SA 515 gr 70 0.0010 20%Sulfamic 0.6 0.2 AISI 1018 0.0010 20% Sulfamic 0.6 0.2 SA 515 gr 700.0015 *HSSR is a sulfuric/glyoxal disclosed in U.S. Pat. No. 4,220,550.

Dynamic tests showed similar but also slightly higher corrosion rates.Accordingly, it is recommended that the inhibitor concentration beincreased to 0.4%.

A corrosion inhibitor prepared in accord with the foregoing pilot plantexample was used to clean a Babock & Wilcox natural circulation boilerand economizer with a nominal capacity of about 22,000 gallons. Tubeanalyses performed before cleaning showed an even deposit of about 16g/ft² containing a mixture of iron, copper and nickel. Cleaning wasundertaken using 3,000 gallons of 40% tetraammonium EDTA at a pH ofabout 9.2 (ChelClean™675) to which 35 gallons of the test inhibitor wasadded. This solution contained about 0.15% by volume inhibitor. Afterchemical injection, the unit was circulated by alternate firing to about320° F. and cooling to about 250° F. An electric pump circulated theeconomizer.

The concentrations of iron and free EDTA in the ChelClean™ 675 cleaningsolution stabilized after about 10hours. These concentrations remainedsubstantially constant for the following 12 hours. The unit was cooledto 150° F. These concentrations are reported in FIG. 26.

Air and 30% hydrogen peroxide were injected through two different portson the lower headers. After initial rapid changes, the copper and freeEDTA concentrations leveled off at about 2 hours. The EMF readings,reflecting the change in the ratio of ferrous to ferric iron, alsochanged rapidly. These values are recorded in FIGS. 27 and 28.

The cleaning was terminated after 3 hours of oxidation with stablecopper and free EDTA concentrations. Following termination of cleaning,the equipment was drained and rinsed. The treated solution was analyzed,and it was determined that the quantity of metals removed closelycorresponded to the amounts predicted from the preliminary scaleanalyses. It was determined that the inhibitor had performedsatisfactorily and provided adequate protection to the unit withoutinterference with copper removal.

The foregoing description of the invention has been directed in primarypart to particular preferred embodiments in accordance with therequirements of the Patent Statute and for purposes of explanation andillustration. It will be apparent, however, to those skilled in the artthat many modifications and changes in the specifically describedmethods and compositions may be made without departing from the truescope and spirit of the invention. Therefore, the invention is notrestricted to the preferred embodiments described and illustrated butcovers all modifications that may fall within the scope of the followingclaims.

What is claimed is:
 1. A low hazard corrosion inhibitor used to inhibitcorrosion of steel in organic acids, chelating agents and sulfuric acid,comprising: about 20-50 percent-by-weight of a mixture of a reactionproduct and a solvent, said solvent selected from the group consistingof propylene glycols, propylene glycol ethers and mixtures thereofwherein said reaction product is formed in said solvent by contacting atertiary ammonium compound with a second compound having the formula RXwhere R is aliphatic, substituted aliphatic or alkyl aryl and X is amonovalent anion; about 1-10 percent-by-weight of a sulphur-containingcompound; about 0-10 percent-by-weight of a nonionic surfactant; and thebalance selected from the group consisting of said solvent, water andmixtures thereof.
 2. The corrosion inhibitor of claim 1 wherein saidmixture of reaction product and solvent has a flash point at least about140° F.
 3. The corrosion inhibitor of claim 1 wherein said tertiaryammonium compound is selected from the group consisting of aromaticammonium compounds and wherein X is a halide and R is selected from thegroup consisting of alkyl and alkyl aryl moieties having from about 6 toabout 18 carbon atoms.
 4. The corrosion inhibitor of claim 1 whereinsaid tertiary ammonium compound is represented by the formula:

wherein each R′₅ independently is —H, —OH, —OR, —OROH, alkyl, alkenyl,alkynyl or halo.
 5. The corrosion inhibitor of claim 1 wherein saidtertiary ammonium compound is selected from the group consisting ofpyridine, quinoline and mixtures thereof and said second compound isselected from the group consisting of alkyl bromides and alkyl arylchlorides.
 6. The corrosion inhibitor of claim 1 wherein said tertiaryammonium compound is pyridine.
 7. The corrosion inhibitor of claim 1wherein said mixture of a reaction product and a solvent were reacted attemperatures greater than about 65° C.
 8. The corrosion inhibitor ofclaim 1 wherein said sulfur compound is selected from the groupconsisting of thiocyanate salts, mercaptoacetic acid, mercaptoaceticacid salts, diethyl thiourea, dibutyl thiourea, diethyl dithio carbamicacid, the salts and methyl derivatives of diethyl dithio carbamic acid,trithio carbamic salts and mixtures thereof.
 9. The corrosion inhibitorof claim 5 wherein said sulfur compound is selected from the groupconsisting of ammonium thiocyanate, diethyl thiourea mercaptoaceticacid, diethyl thiourea mercaptoacetic acid salts and mixtures thereof.10. A low hazard corrosion inhibitor used to inhibit corrosion of steelin organic acids, chelating agents and inorganic acids, comprising:about 20-50 percent-by-weight of a mixture of a reaction product and asolvent, said solvent selected from the group consisting of propyleneglycols, propylene glycol ethers and mixtures thereof and wherein saidreaction product is formed in said solvent by contacting a tertiaryaromatic ammonium compound with a second compound having the formula RXwhere R is aliphatic, substituted aliphatic or alkyl aryl and X is amonovalent anion; about 1-10 percent-by-weight of a sulphur-containingcompound; about 0-10 percent-by-weight of a nonionic surfactant; and thebalance selected from the group consisting of said solvent, water andmixtures thereof.
 11. The corrosion inhibitor of claim 10 wherein X is ahalide and R is selected from the group consisting of alkyl and alkylaryl moieties having from about 6 to about 18 carbon atoms.
 12. Thecorrosion inhibitor of claim 11 wherein said tertiary ammonium compoundis represented by the formula:

wherein each R′₅ independently is —H, —OH, —OR, —OROH, alkyl, alkenyl,alkynyl or halo.
 13. The corrosion inhibitor of claim 12 wherein saidsecond compound is selected from the group consisting of the benzylhalides, naphthyl halides and alkyl halides having from about 7 to about16 carbon atoms.
 14. The corrosion inhibitor of claim 11 wherein saidtertiary ammonium compound is selected from the group consisting ofpyridine, alkyl pyridine, quinoline, alkyl quinoline and mixturesthereof and said second compound is selected from the group consistingof alkyl bromides and alkyl aryl chlorides.
 15. The corrosion inhibitorof claim 14 wherein said tertiary ammonium compound is pyridine.
 16. Thecorrosion inhibitor of claim 15 wherein said second compound is dodecylbromide.
 17. The corrosion inhibitor of claim 14 wherein said solvent isselected from the group consisting of the aliphatic propylene glycolethers having from about 1 to about 4 carbon atoms and the propyleneglycol phenyl ethers.
 18. The corrosion inhibitor of claim 14 whereinsaid solvent is selected from the group consisting of propylene glycolmethyl ether, dipropylene glycol methyl ether, tripropylene glycolmethyl ether, propylene glycol phenyl ether, propylene glycol methylether acetate and dipropylene glycol monomethyl ether acetate.
 19. Thecorrosion inhibitor of claim 16 wherein said solvent is dipropyleneglycol methyl ether.
 20. The corrosion inhibitor of claim 14 whereinsaid sulfur compound is selected from the group consisting ofthiocyanate salts, mercaptoacetic acid, mercaptoacetic acid salts,diethyl thiourea, dibutyl thiourea, diethyl dithio carbamic acid, thesalts and methyl derivatives of diethyl dithio carbamic acid, trithiocarbamic salts and mixtures thereof.
 21. The corrosion inhibitor ofclaim 20 wherein said sulfur compound is selected from the groupconsisting of ammonium thiocyanate, diethyl thiourea mercaptoaceticacid, diethyl thiourea mercaptoacetic acid salts and mixtures thereof.22. The corrosion inhibitor of claim 20 wherein said nonionic surfactantis selected from the group consisting of ethoxylated nonyl phenols,alkyl aryl polyether alcohols, aliphatic polyether alcohols, alcoholethoxy sulfates and alkyl sulfonated diphenyl oxides.
 23. The corrosioninhibitor of claim 14 wherein said mixture reaction product and solventhas a flash point at least about 140° F.
 24. A low hazard corrosioninhibitor used to inhibit corrosion of steel in organic acids, chelatingagents and inorganic acids, comprising: about 20-50 percent-by-weight ofa mixture of a reaction product and a solvent, said solvent selectedfrom the group consisting of the propylene glycol aliphatic ethershaving from about 1 to about 4 carbon atoms and the propylene glycolphenyl ethers wherein said reaction product is formed in said solvent bycontacting a tertiary ammonium compound selected from the groupconsisting of pyridine, alkyl pyridine, quinoline, alkyl quinoline andmixtures thereof with a second compound selected from the groupconsisting of alkyl and alkyl aryl halides having from about 6 to about18 carbon atoms, said tertiary ammonium compound and second compoundpresent in about equal molar ratios; about 1-10 percent-by-weight of asulfur-containing compound having sulfur in the minus two oxidationstate; about 0-10 percent-by-weight of a nonionic surfactant selectedfrom the group consisting of ethoxylated nonyl phenols, alkyl arylpolyether alcohols, aliphatic polyether alcohols, alcohol ethoxysulfates and alkyl sulfonated diphenyl oxides; the balance selected fromthe group consisting of said solvent, water and mixture thereof.
 25. Thelow hazard corrosion inhibitor of claim 24 wherein said solvent isdipropylene glycol methyl ether, said tertiary ammonium compound ispyridine and said second compound is dodecyl bromide.